Subtracting in Weight Painting Adds Material
I would recommend that you never substract any bone weights (unless you know exactly what you are doing, or have all correctly painted weights locked). Blender assigns the lost weight to other bones in proximity, but the program can never know which bone you would want the substracted weight to be on. Instead, add the weight to the bone, that should gain influence in the specific part of the mesh, the weight you add will be substracted from the other bone. It seems, your weight gets transferred to a bone that has transformations, therefore the mesh will displace. Select all bones in posemode and reset them (alt g for position, alt r for rotation and  alt s for scale). If you paint your weights in rest position, nothing should move.